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[英]Referencing multiple row id from 1st table to 2nd table so that it can show all rows from the 1st table every time
[英]How to show id from 1st table from 2 different ids from 2nd table
數據庫是關於公交車運輸的,因此有三個表:
停
stop_id | stop_name
--------------------
1 | station_1
2 | station_2
3 | station_3
路線
route_id | route_num
--------------------
1 | route_1
2 | route_2
3 | route_3
ROUTE_STOP
stop_id | route_id
------------------
1 | 1
2 | 1
1 | 2
3 | 2
1 | 3
2 | 3
3 | 3
因此,第一條路線具有站點1和2,第二條路線具有站點1和3,而第三條路線具有所有站點。
嘗試獲取通過route_num
和route_num
:
SELECT distinct(r.route_num) from STOP s
JOIN ROUTE_STOP rs
ON s.stop_id = rs.stop_id
JOIN ROUTE_STOP r_s
ON rs.stop_id = r_s.stop_id
JOIN ROUTE r
ON rs.route_id = r.route_id
WHERE s.stop_name='station_1' OR s.stop_name='station_3'
AND rs.stop_id <> r_s.stop_id
結果應為route_2和route_3,但不起作用。 如果站點之間沒有路由,則不會有任何結果。
如果2個站點之間沒有路由,如何獲取通過2個站點卻沒有結果的route_num
?
您的查詢應為
SELECT r.route_num from route r
JOIN ROUTE_STOP rs
ON r.route_id = rs.route_id
JOIN STOP s ON rs.stop_id = s.stop_id
WHERE s.stop_name in ('station_1','station_3');
一種方法是聯接表,或者將in
子句與具有group by
並having count()
的組having count()
來查找匹配的組,或者通過route_num進行分組,並使用hading子句來過濾具有所需停靠點的組。 :
-- query 1
SELECT r.route_num
FROM ROUTE r
JOIN ROUTE_STOP rs ON r.route_id = rs.route_id
JOIN STOP s ON rs.stop_id = s.stop_id
WHERE s.stop_name IN ('station_1','station_3')
GROUP BY r.route_num
HAVING COUNT(DISTINCT s.stop_id) = 2;
-- query 2
SELECT r.route_num
FROM ROUTE r
JOIN ROUTE_STOP rs ON r.route_id = rs.route_id
JOIN STOP s ON rs.stop_id = s.stop_id
GROUP BY r.route_num
HAVING (SUM(CASE WHEN s.stop_name = 'station_1' THEN 1 ELSE 0 END) = 1)
AND (SUM(CASE WHEN s.stop_name = 'station_3' THEN 1 ELSE 0 END) = 1);
由於MySQL將布爾表達式的值為1或0,因此您可以將最后一個查詢having
hading子句減少為:
HAVING (SUM(s.stop_name = 'station_1') = 1)
AND (SUM(s.stop_name = 'station_3') = 1);
這兩個查詢均假定在一條路線中可能發生多次停車(對於在同一站點開始和結束的一條路線)。
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